Electronic devices comprising an organic conductor and semiconductor as well as an intermediate buffer layer made of a crosslinked polymer

ABSTRACT

The invention relates to electronic devices whose electronic properties can surprisingly be improved to a significant degree by inserting at least one crosslinkable polymeric buffer layer, preferably a cationically crosslinkable polymeric buffer layer, between the conductive doped polymer and the organic semiconductor layer. Particularly good properties are obtained with a buffer layer in which crosslinking is thermally induced, i.e. by raising the temperature to 50 to 250° C. Alternatively, crosslinking can be radiation-induced by adding a photoacid. Moreover, such a buffer layer can be advantageously applied by means of printing techniques, especially inkjet printing, as the ideal temperature for the thermal treatment is independent of the glass transition temperature of the material. This avoids having to rely on material that has a low molecular weight, making it possible to apply the layer by means of printing techniques. The next layer (the organic semiconductor layer) can also be applied with the aid of different printing techniques, particularly inkjet printing, because the buffer layer is rendered insoluble by the crosslinking process, thus preventing the buffer layer from solubilizing thereafter.

Electronic devices which comprise organic, organometallic and/orpolymeric semiconductors are being used ever more frequently incommercial products or are just about to be introduced onto the market.Examples which may be mentioned here are organic-based charge-transportmaterials (generally hole transporters based on triarylamine) inphotocopiers and organic or polymeric light-emitting diodes (OLEDs orPLEDs) in display devices. Organic solar cells (O-SCs), organicfield-effect transistors (O-FETs), organic thin-film transistors(O-TFTs), organic integrated circuits (O-ICs), organic opticalamplifiers or organic laser diodes (O-lasers) are well advanced at aresearch stage and could achieve major importance in the future.

Many of these devices, irrespective of the application, have thefollowing general layer structure, which is matched correspondingly forthe individual applications:

(1) Substrate

(2) Electrode, frequently metallic or inorganic, but also of organic orpolymeric conducting materials

(3) Charge-injection layer or interlayer for levelling of electrodeunevenness (“planarisation layer”), frequently of a conducting, dopedpolymer

(4) Organic semiconductor

(5) Optionally insulation layer

(6) Second electrode, materials as mentioned under (2)

(7) Circuitry

(8) Encapsulation.

An advantage possessed by many of these organic devices, especiallythose based on polymeric semiconductors, is that they can be producedfrom solution, which is associated with less technical complexity andexpenditure of resources than vacuum processes, as are generally carriedout for low-molecular-weight compounds. For full-colour displays, thethree basic colours (red, green, blue) have to be applied alongside oneanother at high resolution in individual pixels. An analogous situationapplies to electronic circuits with different switching elements.Whereas, in the case of low-molecular-weight molecules that can bevapour-deposited, the individual pixels can be generated by the vapourdeposition of the individual colours through shadow masks, this is notpossible for polymeric materials and materials processed from solution.One solution here consists in applying the active layer (for example thelight-emitting layer in OLEDs/PLEDs; an analogous situation applies tolasers or charge-transport layers in all applications) directly in astructured manner. Recently, various printing techniques, such as, forexample, ink-jet printing (for example EP 0880303), offset printing,etc., in particular, have been considered for this purpose. Intensivework is currently being carried out, in particular, on the developmentof ink-jet printing methods, and considerable advances have recentlybeen achieved here, so that the first commercial products produced inthis way can be expected in the near future.

In devices for organic electronics, an interlayer of a conducting, dopedpolymer is frequently introduced between the electrode (in particularthe anode) and the organic semiconductor and functions ascharge-injection layer (Appl. Phys. Lett. 1997, 70, 2067-2069). Thecommonest of these polymers are polythiophene derivatives (for examplepoly(3,4-ethylenedioxy-2,5-thiophene), PEDOT) and polyaniline (PANI),which are generally doped with polystyrenesulfonic acid or otherpolymer-bound Bronsted acids and are thus brought into a conductingstate. Without wishing to be tied to the correctness of this specifictheory in the following invention, we assume that, on operation of thedevice, protons or other impurities diffuse out of the acidic groupsinto the functional layer, where they are suspected of significantlyinterfering with the functionality of the device. Thus, it is assumedthat these impurities reduce the efficiency and also the service life ofthe devices.

More recent results (M. Leadbeater, N. Patel, B. Tierney, S. O'Connor,I. Grizzi, C. Towns, Book of Abstracts, SID Seattle, 2004) show that theintroduction of a hole-conducting buffer layer between thecharge-injection layer of a conducting doped polymer and the organicsemiconductor results in significantly improved device properties, inparticular in a significantly increased service life. In practice, thegeneral procedure to date has been to apply this buffer layer by asurface-coating method and subsequently to anneal it. Ideally, amaterial is chosen for the buffer layer whose glass-transitiontemperature is below that of the conducting doped polymer, and theannealing is carried out at a temperature above the glass-transitiontemperature of the buffer layer, but below the glass-transitiontemperature of the conducting doped polymer in order to avoid damagingthe latter by the annealing process. In general, this causes a thin partof the buffer layer to become insoluble, generally in the order of 1 to25 nm. For a relatively low glass-transition temperature of the bufferlayer, a material having a relatively low molecular weight is required.However, such a material cannot be applied by ink-jet printing since themolecular weight should be higher for good printing properties.

The soluble part of the buffer layer is then rinsed off by applicationof the organic semiconductor by spin coating, and the organicsemiconductor layer is produced on the insoluble part of the bufferlayer. Thus, a multilayered structure can be produced relatively easilyhere. However, application of the organic semiconductor to the bufferlayer by a printing process is not possible in this way, since thesolvent will then partially dissolve the soluble part of the bufferlayer, and a blend of the material of the buffer layer and the organicsemi-conductor will be formed. The production of structured multilayereddevices is thus not possible in this way.

The production of a device with buffer layer exclusively by ink-jetprinting is thus hitherto still not possible, since on the one hand thebuffer layer cannot be applied by printing techniques owing to the lowmolecular weight and since on the other hand the solution of the organicsemiconductor partially dissolves the buffer layer on application byprinting techniques. However, since printing techniques, in particularink-jet printing, are regarded as a very important method for theproduction of structured devices, but on the other hand the use ofbuffer layers also has considerable potential for further developments,there is thus still a clear need for improvement here.

EP 0637899 proposes electroluminescent arrangements having one or morelayers in which at least one layer is crosslinked and which, inaddition, contain at least one emitter layer and at least onecharge-transport unit per layer. The crosslinking here can proceed bymeans of free radicals, anionically, cationically or via a photoinducedring-closure reaction. Thus, a plurality of layers can be built up oneon top of the other, and the layers can also be structured induced byradiation. However, there is no teaching regarding which of the manifoldcrosslinking reactions can produce a suitable device and how thecrosslinking reaction is best carried out. It is merely mentioned thatfree-radical-crosslinkable units or photocycloaddition-capable groupsare preferred, that auxiliary substances of various types, such as, forexample, initiators, may be present, and that the film is preferablycrosslinked by means of actinic radiation. Neither are suitable deviceconfigurations described. It is thus not clear how many layers thedevice preferably has, how thick these should be, which classes ofmaterial are preferably involved and which thereof are to becrosslinked. It is therefore likewise incomprehensible to the personskilled in the art how the invention described can successfully beimplemented in practice.

ChemPhysChem 2000, 207, describes a triarylamine layer based onlow-molecular-weight compounds which is crosslinked via oxetane groupsas interlayer between a conducting doped polymer and an organicluminescent semiconductor. Relatively high efficiency was obtained here.A device of this type cannot be produced by printing processes, inparticular ink-jet printing, since the low-molecular-weight triarylaminederivatives do not produce sufficiently viscous solutions beforecrosslinking.

Surprisingly, it has now been found that the electronic properties ofthe devices can be significantly improved if at least one crosslinkablepolymeric buffer layer, preferably a cationically crosslinkablepolymeric buffer layer, is introduced between the conducting dopedpolymer and the organic semiconductor layer. Particularly goodproperties are obtained in the case of a buffer layer whose crosslinkingis thermally induced, i.e. by increasing the temperature to 50-250° C.However, the crosslinking can also be initiated, for example, byirradiation with addition of a photoacid. In addition, a buffer layer ofthis type can advantageously also be applied by printing techniques, inparticular ink-jet printing, since the ideal temperature for the thermaltreatment here is independent of the glass-transition temperature of thematerial. This means that it is not necessary to rely on materials oflow molecular weight, which in turn facilitates application of the layerby printing techniques. Since the buffer layer becomes insoluble due tothe crosslinking, the subsequent layer (the organic semiconductor layer)can also be applied by various printing techniques, in particularink-jet printing, since there is then no risk of partial dissolution ofthe buffer layer and blend formation.

The invention therefore relates to organic electronic devices comprisingcathode, anode, at least one layer of a conducting, doped polymer and atleast one layer of an organic semiconductor, characterised in that atleast one conducting or semiconducting, preferably semiconducting,crosslinkable polymeric buffer layer, preferably a cationicallycrosslinkable buffer layer, is introduced between these two layers.

The semiconducting polymeric buffer layer is, for the crosslinking,preferably admixed with less than 3% by weight of a photoacid,particularly preferably less than 1 % by weight, very particularlypreferably with no photoacid.

Preference is furthermore given to a polymeric crosslinkable bufferlayer whose crosslinking in the corresponding device arrangement can beinduced thermally, i.e. by increasing the temperature without additionof further auxiliary substances, such as, for example, photoacids.

A photoacid is a compound which liberates a protic acid through aphotochemical reaction on irradiation with actinic radiation. Examplesof photoacids are 4-(thiophenoxyphenyl)diphenylsulfoniumhexafluoroantimonate,(4-[(2-hydroxy-tetradecyl)oxyl]phenyl}phenyliodoniumhexafluoroantimonate and others, as described, for example, in EP1308781. The photoacid can be added for the crosslinking reaction,preferably with a proportion of about 0.5 to 3% by weight beingselected, but does not necessarily have to be added.

For the purposes of this invention, electronic devices are organic orpolymeric light-emitting diodes (OLEDs, PLEDs, for example EP 0 676 461,WO 98/27136), organic solar cells (O-SCs, for example WO 98/48433, WO94/05045), organic field-effect transistors (O-FETs, for example U.S.Pat. No. 5,705,826, U.S. Pat. No. 5,596,208, WO 00/42668), organicthin-film transistors (O-TFTs), organic integrated circuits (O -ICs, forexample WO 95/31833, WO 99/10939), organic field-quench elements (FQDs,for example US 2004/017148), organic optical amplifiers or organic laserdiodes (O-lasers, for example WO 98/03566). For the purposes of thisinvention, organic means that at least one layer of an organicconducting doped polymer, at least one conducting or semiconductingpolymeric buffer layer and at least one layer comprising at least oneorganic semiconductor are present; it is also possible for furtherorganic layers (for example electrodes, etc.) to be present. However, itis also possible for layers which are not based on organic materials,such as, for example, further interlayers or electrodes, to be present.

In the simplest case, the electronic device is constructed fromsubstrate (usually glass or plastic film), electrode, interlayer of aconducting, doped polymer, crosslinkable buffer layer according to theinvention, organic semi-conductor and counterelectrode. This device iscorrespondingly (depending on the application) structured, provided withcontacts and finally hermetically sealed since the service life ofdevices of this type is drastically shortened in the presence of waterand/or air. It may also be preferred here to use a conducting, dopedpolymer as electrode material for one or both electrodes and not tointroduce an interlayer of conducting, doped polymer. For applicationsin O-FETs and O-TFTs, it is also necessary that, in addition toelectrode and counterelectrode (source and drain), the structure alsocontains a further electrode (gate), which is separated from the organicsemiconductor by an insulator layer having a generally high (or morerarely low) dielectric constant. In addition, it may be appropriate tointroduce further layers into the device. The electrodes are selected sothat their potential corresponds as well as possible to the potential ofthe adjacent organic layer in order to ensure the most efficientelectron or hole injection possible. The cathode is preferably metalshaving a low work function, metal alloys or multilayered structures ofvarious metals, such as, for example, alkaline-earth metals, alkalimetals, main-group metals or lanthanoids (for example Ca, Ba, Mg, Al,In, Mg, Yb, Sm, etc.). In the case of multilayered structures, furthermetals which have a relatively high work function, such as, for example,Ag, may also be used in addition to the said metals, in which casecombinations of the metals, such as, for example, Ca/Ag or Ba/Ag, aregenerally used.

It may also be preferred to introduce a thin interlayer of a materialhaving a high dielectric constant between a metallic cathode and theorganic semiconductor. Suitable for this purpose are, for example,alkali metal or alkaline-earth metal fluorides, but also thecorresponding oxides (for example LiF, Li₂O, BaF₂, MgO, NaF, etc.). Thelayer thickness of this dielectric layer is preferably between 1 and 10nm.

The anode is preferably materials having a high work function. The anodepreferably has a potential of greater than 4.5 eV vs. vacuum. Suitablefor this purpose are on the one hand metals having a high redoxpotential, such as, for example, Ag, Pt or Au. Metal/metal oxideelectrodes (for example Al/Ni/NiOX, Al/Pt/PtOx) may also be preferred.

For some applications, at least one of the electrodes must betransparent in order to facilitate either irradiation of the organicmaterial (O-SC) or the coupling out of light (OLED/PLED, O-LASER). Apreferred construction uses a trans-parent anode. Preferred anodematerials here are conducting mixed metal oxides. Particular preferenceis given to indium-tin oxide (ITO) or indium-zinc oxide (IZO).Preference is furthermore given to conducting, doped organic materials,in particular conducting doped polymers.

Suitable as charge-injection layer on the anode are various doped,conducting polymers. Preference is given to polymers which have aconductivity of >10⁻⁸ S/cm, depending on the application. The potentialof the layer is preferably 4 to 6 eV vs. vacuum. The layer thickness ispreferably between 10 and 500 nm, particularly preferably between 20 and250 nm. Particular preference is given to the use of derivatives ofpolythiophene (in particular poly(3,4-ethylenedioxy-2,5-thiophene),PEDOT) and polyaniline (PANI). The doping is generally carried out bymeans of acids or oxidants. The doping is preferably carried out bymeans of polymer-bound Bronsted acids. For this purpose, particularpreference is given to polymer-bound sulfonic acids, in particularpoly(styrenesulfonic acid), poly(vinylsulfonic acid) and PAMPSA(poly-(2-acrylamido-2-methylpropanesulfonic acid)). The conductingpolymer is generally applied from an aqueous solution or dispersion andis insoluble in organic solvents. This enables the subsequent layer tobe applied without problems from organic solvents.

The organic semiconductor preferably comprises at least one polymericcompound. This can be a single polymeric compound or a blend of two ormore polymeric compounds or a blend of one or more polymeric compoundswith one or more low-molecular-weight organic compounds. The organicsemiconductor layer can preferably be applied by various printingprocesses, in particular by ink-jet printing processes. For the purposesof this invention, an organic material is taken to mean not only purelyorganic compounds, but also organometallic compounds and metalcoordination compounds with organic ligands. In the case of luminescentcompounds, these can either fluoresce or phosphoresce, i.e. emit lightfrom the singlet or triplet state. The polymeric materials here may beconjugated, partially conjugated or non-conjugated. Preference is givento conjugated materials. For the purposes of this invention, conjugatedpolymers are polymers which contain in the main chain principallysp²-hybridised carbon atoms, which may also be replaced by correspondinghetero atoms. Furthermore, the term conjugated is likewise used in thisapplication text if, for example, arylamine units and/or certainheterocycles (i.e. conjugation via N, O or S atoms) and/ororganometallic complexes (i.e. conjugation via the metal atom) arepresent in the main chain. Typical representatives of conjugatedpolymers as can be used, for example, in PLEDs or O-SCs arepoly-para-phenylenevinylenes (PPVs), polyfluorenes,polyspirobifluorenes, polydihydro-phenanthrenes, polyindenofluorenes,systems based in the broadest sense on poly-p-phenylenes (PPPs), andderivatives of these structures. Of particular interest for use inO-FETs are materials having high charge-carrier mobility. These are, forexample, oligo- or poly(triarylamines), oligo- or poly(thiophenes) andcopolymers containing a high proportion of these units. The layerthickness of the organic semiconductor is preferably 10-500 nm,particularly preferably 20-250 nm, depending on the application.

Without wishing to be tied to a certain theory, we assume that theprotons or other cationic impurities present in the conducting dopedpolymer are problematic and diffusion thereof out of the doped polymeris suspected of being the limiting factor for the service life of theelectronic device. In addition, hole injection from the doped polymersinto the organic semiconductor is often unsatisfactory.

A polymeric buffer layer is therefore introduced between the conducting,doped polymer and the organic semiconductor which carries crosslinkableunits, in particular cationically crosslinkable units, so that it canaccommodate low-molecular-weight, cationic species and intrinsiccationic charge carriers which are able to diffuse out of theconducting, doped polymer. However, other crosslinkable groups, forexample groups which are crosslinkable anionically or by means of freeradicals, are also possible and in accordance with the invention. Thislayer furthermore serves for improved hole injection and as electronblocking layer. For the buffer layer, preference is given to the use ofconjugated crosslinkable polymers. The molecular weight of the polymersused for the buffer layer before crosslinking is preferably in the rangefrom 50 to 500 kg/mol, particularly preferably in the range from 200 to250 g/mol. This molecular-weight range has proven particularly suitablefor application by ink-jet printing. For other printing techniques,however, other molecular-weight ranges may also be preferred. The layerthickness of the buffer layer is preferably in the range from 1 to 300nm, particularly preferably in the range from 15 to 200 nm, veryparticularly preferably in the range from 40 to 100 nm. The potential ofthe buffer layer is preferably between the potential of the conducting,doped polymer and that of the organic semiconductor in order to improvethe charge injection. This can be achieved through a suitable choice ofthe materials for the buffer layer and suitable substitution of thematerials. It may also be preferred to admix further crosslinkablelow-molecular-weight compounds with the polymeric material of the bufferlayer. This may be appropriate in order, for example, to reduce theglass-transition temperature of the mixture and thus to facilitatecrosslinking at a lower temperature.

Preferred materials for the buffer layer are derived fromhole-conducting materials. Particularly preferably suitable for thispurpose are cationically crosslinkable materials based on triarylamine,based on thiophene, based on triarylphosphine or combinations of thesesystems, where copolymers thereof with other structures, for examplefluorenes, spirobifluorenes, dihydrophenanthrenes, indenofluorenes,etc., are also suitable materials if an adequately high proportion ofthe above-mentioned hole-conducting units is used. The proportion ofhole-conducting units in the polymer is particularly preferably at least10 mol %. The potentials of these compounds can be adjusted throughsuitable substitution. Thus, compounds having a lower HOMO (=highestoccupied molecular orbital) are obtained through the introduction ofelectron-withdrawing substituents (for example F, Cl, CN, etc.), while ahigher HOMO is achieved by electron-donating substituents (for examplealkoxy groups, amino groups, etc.).

Without wishing to be tied to a certain theory, we assume that acationically crosslinkable buffer layer is able to accommodate diffusingcationic species, in particular protons, through the crosslinkingreaction being initiated thereby; on the other hand, the crosslinkingsimultaneously makes the buffer layer insoluble, so that subsequentapplication of the organic semiconductor from the usual organic solventspresents no problems. The crosslinked buffer layer represents a furtherbarrier against diffusion. Preferred polymerisable groups are thereforecationically crosslinkable groups, in particular:

1) electron-rich olefin derivatives,

2) heteronuclear multiple bonds with hetero atoms or hetero groups and

3) rings containing hetero atoms (for example O, S, N, P, Si, etc.)which react by cationic ring-opening polymerisation.

Electron-rich olefin derivatives and compounds containing heteronuclearmultiple bonds with hetero atoms or hetero groups are preferably thoseas described in H.-G. Elias, Makromoleküle [Macromolecules], Volume 1.Fundamentals: Structure—Synthesis—Properties, Hüthig & Wepf Verlag,Basle, 5th Edition, 1990, pp. 392-404, without wishing thereby torestrict the variety of possible compounds.

Preference is given to organic materials in which at least one H atomhas been replaced by a group which reacts by cationic ring-openingpolymerisation. A general review of cationic ring-opening polymerisationis given, for example, by E. J. Goethals et al., “Cationic Ring OpeningPolymerisation” (New Methods Polym. Synth. 1992, 67-109). Generallysuitable for this purpose are non-aromatic cyclic systems in which oneor more ring atoms are, identically or differently, O, S, N, P, Si, etc.Preference is given here to cyclic systems having 3 to 7 ring atoms inwhich 1 to 3 ring atoms are, identically or differently, O, S or N.Examples of such systems are unsubstituted or substituted cyclic amines(for example aziridine, azeticine, tetrahydropyrrole, piperidine),cyclic ethers (for example oxirane, oxetane, tetrahydrofuran, pyran,dioxane), and also the corresponding sulfur derivatives, cyclic acetals(for example 1,3-dioxolane, 1,3-dioxepan, trioxane), lactones, cycliccarbonates, but also cyclic structures which contain differentheteroatoms in the ring (for example oxazolines, dihydrooxazines,oxazolones). Preference is furthermore given to cyclic siloxanes having4 to 8 ring atoms.

Very particular preference is given to polymeric organic materials inwhich at least one H atom has been replaced by a group of the formula(I), formula (II) or formula (III)

where:

R¹ is on each occurrence, identically or differently, hydrogen, astraight-chain, branched or cyclic alkyl, alkoxy or thioalkoxy grouphaving 1 to 20 C atoms, an aromatic or heteroaromatic ring system having4 to 24 aromatic ring atoms or an alkenyl group having 2 to 10 C atoms,in which one or more hydrogen atoms may be replaced by halogen, such asCl and F, or CN, and one or more non-adjacent C atoms may be replaced by—O—, —S—, —CO—, —COO— or —O—CO—; a plurality of radicals R¹ here mayalso form a mono- or polycyclic, aliphatic or aromatic ring system withone another or with R², R³ and/or R⁴;

R² is on each occurrence, identically or differently, hydrogen, astraight-chain, branched or cyclic alkyl group having 1 to 20 C atoms,an aromatic or heteroaromatic ring system having 4 to 24 aromatic ringatoms or an alkenyl group having 2 to 10 C atoms, in which one or morehydrogen atoms may be replaced by halogen, such as Cl and F, or CN, andone or more non-adjacent C atoms may be replaced by —O—, —S—, —CO—,—COO— or —O—CO—; a plurality of radicals R² here may also form a mono-or polycyclic, aliphatic or aromatic ring system with one another orwith R¹, R³and/or R⁴;

X is on each occurrence, identically or differently, —O—, —S—, —CO—,—COO—, —O—CO— or a divalent group —(CR³R⁴)_(n)—;

Z is on each occurrence, identically or differently, a divalent group—(CR³R⁴ )_(n)—;

R³, R⁴ is on each occurrence, identically or differently, hydrogen, astraight-chain, branched or cyclic alkyl, alkoxy, alkoxyalkyl orthioalkoxy group having 1 to 20 C atoms, an aromatic or heteroaromaticring system having 4 to 24 aromatic ring atoms or an alkenyl grouphaving 2 to 10 C atoms, in which one or more hydrogen atoms may also bereplaced by halogen, such as Cl or F, or CN; two or more radicals R³ orR⁴ here may also form a ring system with one another or also with R¹ orR²;

n is on each occurrence, identically or differently, an integer between0 and 20, preferably between 1 and 10, in particular between 1 and 6;with the proviso that the number of these groups of the formula (I) orformula (II) or formula (III) is limited by the maximum number ofavailable, i.e. substitutable, H atoms.

The crosslinking of these units can be carried out, for example, bythermal treatment of the device at this stage. A photoacid for thecrosslinking can optionally also be added. Preference is given tothermal crosslinking without addition of a photoacid. Further auxiliarysubstances may likewise optionally be added, such as, for example, saltsor acids, which are added both to the buffer layer and also to theconducting polymer layer. This crosslinking is preferably carried out ata temperature of 80 to 200° C. and for a duration of 0.1 to 60 minutesin an inert atmosphere. This crosslinking is particularly preferablycarried out at a temperature of 100 to 180° C. and for a duration of 1to 30 minutes in an inert atmosphere.

The invention furthermore relates to the use of crosslinkable polymersfor the production of a buffer layer according to the inventiondescribed above.

For the production of the devices, the following general process, whichshould be adapted correspondingly to the individual case without furtherinventive step, is generally used:

-   -   A substrate (for example glass or also a plastic) is coated with        the anode (for example indium-tin oxide, ITO, etc.). The anode        is subsequently structured (for example photolithographically)        and connected in accordance with the desired application. The        anode-coated, pre-cleaned substrate is treated with ozone or        with oxygen plasma or irradiated briefly with an excimer lamp.    -   A conducting polymer, for example a doped polythiophene (PEDOT)        or polyaniline derivative (PANI), is subsequently applied in a        thin layer to the ITO substrate by spin coating or other coating        methods.    -   The crosslinkable buffer layer according to the invention is        applied to this layer. To this end, the corresponding compound        is firstly dissolved in a solvent or solvent mixture, preferably        under a protective gas, and filtered. Suitable solvents are        aromatic liquids (for example toluene, xylenes, anisole,        chlorobenzene), cyclic ethers (for example dioxane,        methyidioxane, THF) or amides (for example NMP, DMF), but also        solvent mixtures as described in WO 02/072714. The supports        described above can be coated over the entire surface with these        solutions, for example by spin-coating methods, or in a        structured manner by printing processes, in particular ink-jet        printing. The crosslinking can then be carried out (in the case        of the use of cationically crosslinkable groups) by heating the        device in an inert atmosphere at this stage. A photoacid can        also be added and the crosslinking initiated by irradiation,        also enabling structuring to be achieved. Depending on the type        of crosslinkable group, the crosslinking can be initiated in        various ways. Rinsing with a solvent, for example THF, can        optionally subsequently be carried out. Finally, drying is        carried out.    -   A solution of an organic semiconductor is applied thereto.        Suitable for the production of structured devices here are, in        particular, printing processes, for example ink-jet printing.        The crosslinking of the buffer layer makes application of the        organic semiconductor from solution possible without problems        without the buffer layer being dissolved in the process.    -   Further functional layers, such as, for example,        charge-injection or -transport layers or hole-blocking layers,        can optionally be applied to these polymer layers, for example        from solution, but also by vapour deposition.    -   A cathode is subsequently applied. This is carried out in        accordance with the prior art by a vacuum process and can take        place, for example, either by thermal vapour deposition or by        plasma spraying (sputtering).    -   Since many of the applications react sensitively to water,        oxygen or other constituents of the atmosphere, effective        encapsulation of the device is vital.    -   The structure described above is adapted and optimised        correspondingly for the individual applications without further        inventive step and can be used in general for various        applications, such as organic and polymeric light-emitting        diodes, organic solar cells, organic field-effect transistors,        organic thin-film transistors, organic integrated circuits,        organic optical amplifiers or organic laser diodes.

Surprisingly, this crosslinkable buffer layer that is introduced betweenthe conducting, doped polymer and the organic semiconductor offers thefollowing advantages:

1) Introduction of the crosslinkable buffer layer according to theinvention improves the opto-electronic properties of the electronicdevice compared with a device comprising no buffer layer of this type.Thus, higher efficiency and a longer service life are observed.

2) Crosslinking of the buffer layer enables thicker buffer layers to beproduced than is possible with uncrosslinked buffer layers, which onlyform a thin insoluble layer by annealing and rinsing. With thesethicker, crosslinked buffer layers, better device results are obtainedthan with uncrosslinked, thinner buffer layers in accordance with theprior art.

3) Cationic crosslinking of the buffer layer overcomes the reliance on alow glass-transition temperature and thus on a low-molecular-weightmaterial for the annealing. The fact that high-molecular-weightmaterials can now also be used for this purpose enables the buffer layerto be applied by ink-jet printing.

4) Crosslinking of the buffer layer gives an insoluble layer. Thisenables the subsequent layer of the organic semiconductor to be appliedby a printing process, for example ink-jet printing, without the bufferlayer being dissolved and a blend of the material of the buffer layerand the organic semiconductor forming. This is not possible with bufferlayers in accordance with the prior art and is of major importance forthe production of structured devices.

The present invention is explained in greater detail by the followingexamples, without wishing to be restricted thereto. In these examples,only organic and polymeric light-emitting diodes are discussed. However,the person skilled in the art will be able to produce further electronicdevices, such as, for example, O-SCs, O-FETs, O-TFTs, O-ICs, organicoptical amplifiers and O-lasers, to mention but a few furtherapplications, from the examples listed without inventive step.

EXAMPLES Example 1 Layer Thickness of the Crosslinkable Buffer Layer

A layer of crosslinkable buffer layer A (polymer having structure A)with a thickness of 60 nm was applied by spin coating to a device havingthe following layer structure: glass//150 nm ITO//H80 nm PEDOT (annealedat 200° C. for 10 min.). The device was subsequently heated at 180° C.for 1 h. PEDOT is a polythiophene derivative (Baytron P4083 from H. C.Starck, Goslar). The device was washed with toluene by spinning, and theresultant layer thickness was measured. A layer thickness of 60 nm (±2nm) was determined for the buffer layer.

Example 2 (Comparison) Layer Thickness of the Uncrosslinkable BufferLayer

A layer of uncrosslinkable buffer layer B (polymer having structure B)with a thickness of 60 nm was applied by spin coating to a device havingthe following layer structure: glass//150 nm ITO//80 nm PEDOT (annealedat 200° C. for 10 min.). The device was subsequently heated at 180° C.for 1 h. The device was washed with toluene by spinning, and theresultant layer thickness was measured. A layer thickness of 10 nm (±1nm) was determined for the buffer layer.

Example 3 OLED Having a Crosslinkable Buffer Layer

80 nm of the blue-emitting polymer C were applied by spin-coating to thedevice having a 60 nm buffer layer A. The total layer thickness measured(PEDOT+buffer layer+emitting polymer) was 220 nm (±4 nm). The cathodeused was in all cases Ba from Aldrich and Ag from Aldrich. The way inwhich PLEDs can be produced in general is described in detail, forexample, in WO 04/037887 and the literature cited therein.

A maximum efficiency of 4.1 cd/A and a service life of 640 h (beginningfrom 800 cd/m²) were measured for the device.

Example 4 (Comparison) OLED Having an Uncrosslinkable Buffer Layer

80 nm of the blue-emitting polymer C were applied by spin coating to thedevice having a 60 nm buffer layer B (not rinsed with toluene). Thetotal layer thickness measured (PEDOT+buffer layer+emitting polymer) was170 nm (±3 nm).

A maximum efficiency of 3.5 cd/A and a service life of 420 h (beginningfrom 800 cd/m²) were measured for the device.

Example 5 (Comparison) OLED Without a Buffer Layer

80 nm of the blue-emitting polymer C were applied by spin coating to adevice consisting of glass/150 nm ITO//80 nm PEDOT (annealed at 200° C.for 10 min.). The total layer thickness measured (PEDOT+bufferlayer+emitting polymer) was 160 nm (±3 nm).

A maximum efficiency of 3.1 cd/A and a service life of 180 h (beginningfrom 800 cd/M²) were measured for the device.

Polymers A, B and C and the corresponding monomers were synthesised asdescribed in WO 02/10129, WO 03/020790 and WO 03/048225. Thecompositions and structures of polymers A, B and C are shown below forreasons of clarity:

As is thus evident from Example 1 and Comparative Example 2, thecrosslinkable buffer layer enables the production of thicker, insolublelayers, to which the light-emitting polymer can then be applied. Inparticular, it is also possible to apply polymer C to crosslinkedpolymer A by printing techniques since the latter is no longer dissolvedby solvents, while it is not possible to apply polymer C touncrosslinked polymer B since the latter is dissolved thereby.

It is likewise evident from Example 3 and Comparative Example 4 thatpolymer C exhibits higher efficiency and a longer service life if it isused with a buffer layer, in contrast to Comparative Example 5, in whichit was applied directly to PEDOT without a buffer layer. It is strikinghere that the use of a crosslinkable buffer layer leads to significantlybetter results (higher efficiency, longer service life) than the use ofthe uncrosslinkable buffer layer.

1. Organic electronic devices comprising cathode, anode, at least onelayer of a conducting, doped polymer and at least one layer of anorganic semiconductor, characterised in that at least one conducting orsemiconducting crosslinkable polymeric buffer layer is introducedbetween the doped polymer and the organic semiconductor.
 2. Organicelectronic device according to claim 1, characterised in that it is anorganic or polymeric light-emitting diode (OLED, PLED), organic solarcell (O-SC), organic field-effect transistor (O-FET), organic thin-filmtransistor (O-TFT), organic integrated circuit (O-IC), organicfield-quench element (FQD), organic optical amplifier or organic laserdiode (O-laser).
 3. Organic electronic device according to claim 1,characterised in that the conducting doped polymer used is a derivativeof polythiophene or polyaniline, and the doping is carried out by meansof polymer-bound acids or by means of oxidants.
 4. Organic electronicdevice according to , characterised in that the organic semiconductorcomprises at least one polymeric compound.
 5. Organic electronic deviceaccording to claim 4, characterised in that the polymeric compound is aconjugated polymer.
 6. Organic electronic device according to claim 5,characterised in that the organic semiconductor employed is a conjugatedpolymer from the classes of the poly-para-phenylenevinylenes (PPVs),polyfluorenes, polyspirobifluorenes, polydihydrophenanthrenes,polyindenofluorenes, systems based in the broadest sense onpoly-p-phenylenes (PPPs), and derivatives of these structures. 7.Organic electronic device according to claim 1, characterised in thatthe organic semiconductor is applied by a printing process.
 8. Organicelectronic device claim 1, characterised in that the polymericcrosslinkable buffer layer has a molecular weight in the range from 50to 500 kg/mol before crosslinking.
 9. Organic electronic deviceaccording to claim 1, characterised in that the polymeric crosslinkablebuffer layer is applied by a printing process.
 10. Organic electronicdevice according to claim 1, characterised in that the layer thicknessof the polymeric crosslinkable buffer layer is in the range from 1 to300 nm.
 11. Organic electronic device according to claim 1,characterised in that the buffer layer is built up from a conjugatedpolymer.
 12. Organic electronic device according to claim 1,characterised in that the materials of the buffer layer aretriarylamine, thiophene or triarylphosphine polymers or combinations ofthese systems.
 13. Organic electronic device according to claim 1,characterised in that the materials of the buffer layer are copolymersof triarylamine, thiophene and/or triarylphosphine derivatives withfluorenes, spirobifluorenes, dihydrophenanthrenes and/orindenofluorenes.
 14. Organic electronic device according to claim 1,characterised in that the buffer layer is cationically crosslinkable.15. Organic electronic device according to claim 14, characterised inthat the crosslinkable groups are selected from electron-rich olefinderivatives, heteronuclear multiple bonds with hetero atoms or heterogroups or rings containing hetero atoms which react by cationicring-opening polymerisation.
 16. Organic electronic device according toclaim 15, characterised in that at least one H atom in the materials ofthe buffer layer has been replaced by a heterocyclic compound whichreacts by cationic ring-opening polymerisation.
 17. Organic electronicdevice according to claim 16, characterised in that at least one H atomin the materials of the buffer layer has been replaced by a group of theformula (I), formula (II) or formula (III)

where: R¹ is on each occurrence, identically or differently, hydrogen, astraight-chain, branched or cyclic alkyl, alkoxy or thioalkoxy grouphaving 1 to 20 C atoms, an aromatic or heteroaromatic ring system having4 to 24 aromatic ring atoms or an alkenyl group having 2 to 10 C atoms,in which one or more hydrogen atoms may be replaced by halogen, or CN,and one or more non-adjacent C atoms may be replaced by —O—, —S—, —CO—,—COO— or —O—CO—; a plurality of radicals R¹ here may also form a mono-or polycyclic, aliphatic or aromatic ring system with one another orwith R², R³ and/or R⁴; R² is on each occurrence, identically ordifferently, hydrogen, a straight-chain, branched or cyclic alkyl grouphaving 1 to 20 C atoms, an aromatic or heteroaromatic ring system having4 to 24 aromatic ring atoms or an alkenyl group having 2 to 10 C atoms,in which one or more hydrogen atoms may be replaced by halogen, or CN,and one or more non-adjacent C atoms may be replaced by —O—, —S—, —CO—,—COO— or —O—CO—; a plurality of radicals R² here may also form a mono-or polycyclic, aliphatic or aromatic ring system with one another orwith R¹, R³ and/or R⁴; X is on each occurrence, identically ordifferently, —O—, —S—, —CO—, —COO—, —O—CO— or a divalent group—(CR³R⁴)_(n)—; Z is on each occurrence, identically or differently, adivalent group —(CR³R⁴)_(n)—; R³, R⁴ is on each occurrence, identicallyor differently, hydrogen, a straight-chain, branched or cyclic alkyl,alkoxy, alkoxyalkyl or thioalkoxy group having 1 to 20 C atoms, anaromatic or heteroaromatic ring system having 4 to 24 aromatic ringatoms or an alkenyl group having 2 to 10 C atoms, in which one or morehydrogen atoms may also be replaced by halogen, or CN; two or moreradicals R³ or R⁴ here may also form a ring system with one another oralso with R¹ or R², n is on each occurrence, identically or differently,an integer between 0 and 20, with the proviso that the number of thesegroups of the formula (I) or formula (II) or formula (III) is limited bythe maximum number of available, i.e. substitutable, H atoms. 18.Organic electronic device according to claim 1, characterised in thatthe crosslinking of the buffer layer is initiated by addition of aphotoacid.
 19. Organic electronic device according to claim 1,characterised in that the crosslinking of the buffer layer is carriedout by thermal treatment without addition of a photoacid.
 20. Organicelectronic device according to claim 19, characterised in that thecrosslinking is carried out at a temperature of 80 to 200° C. and for aduration of 0.1 to 60 minutes in an inert atmosphere.
 21. (canceled) 22.A buffer layer which comprises at least one conducting or semiconductingcrosslinkable polymer.
 23. Organic electronic device according to claim17, wherein R¹ is on each occurrence, identically or differently,hydrogen, a straight-chain, branched or cyclic alkyl, alkoxy orthioalkoxy group having 1 to 20 C atoms, an aromatic or heteroaromaticring system having 4 to 24 aromatic ring atoms or an alkenyl grouphaving 2 to 10 C atoms, in which one or more hydrogen atoms may bereplaced by Cl, F, or CN, and one or more non-adjacent C atoms may bereplaced by —O—, —S—, —CO—, —COO— or —O—CO—; a plurality of radicals R¹here may also form a mono- or polycyclic, aliphatic or aromatic ringsystem with one another or with R², R³ and/or R⁴; R² is on eachoccurrence, identically or differently, hydrogen, a straight-chain,branched or cyclic alkyl group having 1 to 20 C atoms, an aromatic orheteroaromatic ring system having 4 to 24 aromatic ring atoms or analkenyl group having 2 to 10 C atoms, in which one or more hydrogenatoms may be replaced by Cl, F, or CN, and one or more non-adjacent Catoms may be replaced by —O—, —S—, —CO—, —COO— or —O—CO—; a plurality ofradicals R² here may also form a mono- or polycyclic, aliphatic oraromatic ring system with one another or with R¹, R³ and/or R⁴; R³, R⁴is on each occurrence, identically or differently, hydrogen, astraight-chain, branched or cyclic alkyl, alkoxy, alkoxyalkyl orthioalkoxy group having 1 to 20 C atoms, an aromatic or heteroaromaticring system having 4 to 24 aromatic ring atoms or an alkenyl grouphaving 2 to 10 C atoms, in which one or more hydrogen atoms may also bereplaced by Cl, F, or CN; two or more radicals R³ or R⁴ here may alsoform a ring system with one another or also with R¹ or R², n is on eachoccurrence, identically or differently, an integer between 1 and 6.